The intestinal microflora is known to biotransform steroid hormones and bile acids into a variety of metabolites. Moreover, certain steroid metabolites generated by intestinal bacteria have been implicated as playing important roles colon carcinogenesis, cholesterol homeostasis and gallstone formation in man. The overall objective of this proposed reseach is to delineate the role of intestinal bacterial steroid biotransformations on overall human steroid metabolism. The first goal will be to purify and characterize 21-dehydroxylase from the human intestinal anaerobic, Eubacterium lentum and to elucidate the effects of H2 and Eh on the rates of 21-dehydroxylation in whole cells. The second goal will be to determine if human fecal suspensions and pure cultures of intestinal bacteria have C17-C20 lyase (demolase) activity. The third goal will be to determine if human fecal suspensions and pure cultures of intestinal bacteria can biotransform Vitamin D3 and to characterize the Vitamin D3 derivative(s) by their U.V. absorption spectra and by mass spectrometry. The fourth goal will be to purify and characterize the enzyme(s) involved in the 7-alpha-dehydroxlyation of primary bile acids from a Eubacterium species V.P.I. 12708. The final goal will be to isolate and biochemically characterize 7-alpha-dehydroxylase negative mutant strains of Eubacterium species V.P.I. 12708.